Functionalisation of silica gel with cyclic and acyclic Schiff bases and related d- and/or f-metal complexes

Abstract

Two different synthetic pathways were devised in order to graft on silica gel organic moieties, containing macroacyclic or macrocyclic compartimental ligands, formed of an inner N 3O 2 or N 2O 2 Schiff base site, able to coordinate d metal ions, and one adjacent O 2O 2 or O 2O 4 crown ether-like chamber suitable for hosting f ions, in the terminal part. These materials can bind d metal ions into the amine–imine moiety. Their subsequent reaction with varying amounts of gadolinium(III) invariantly gives a system in which two grafted copper complexes coordinate only one gadolinium(III) ion with their oxygen-containing chambers, giving rise to a trinuclear Cu 2Gd entity. According to a third strategy, some mono- and heterobi-metallic macrocyclic complexes were transferred from a water/methanol solution into functionalised silica platforms by coordinating their metal ions to the donor group of one silica-anchored organic residual. UV–Vis spectra of solutions containing these metal complexes gave a clear indication of the selective coordinating ability of the donor group towards 3d or 4f metal ions.